Achatina fulica is a species of land snail in the family Achatinidae, known commonly as the giant African snail or giant African land snail.[1] Outside of its native range it thrives in many types of habitat in areas with mild climates, it feeds voraciously and is a vector for plant pathogens, causing severe damage to agricultural crops and native plants, it competes with native snail taxa, it is a nuisance pest of urban areas, and it spreads human disease.[1] It is listed as one of the top 100 invasive species in the world.[2]

The species has recently been observed in Bhutan (Gyelposhing, Mongar), where it is an invasive species. It has begun to attack agricultural fields and flower gardens. It is believed there that dogs have died as a result of consuming the snail.

Description[edit]

The adult snail is around 7 centimetres (2.8 in) in height and 20 centimetres (7.9 in) or more in length.

The shell has a conical shape, being about twice as high as it is broad. Either clockwise (dextral) or counter-clockwise (sinistral) directions can be observed in the coiling of the shell, although the right-handed (dextral) cone is the more common. Shell colouration is highly variable, and dependent on diet. Typically, brown is the predominant colour and the shell is banded.[8] The shell is particularly tough and has the highest heavy metal content of any snail species.[9]

Apertural view of the shell

Lateral view of the shell

Abapertural view of the shell

Ecology[edit]

Habitat[edit]

The giant African snail is native to East Africa, and can be traced back to Kenya and Tanzania. It is a highly invasive species, and colonies can be formed from a single gravid individual. In many places, release into the wild is illegal. Nonetheless, the species has established itself in some temperate climates and its habitat now includes most regions of the humid tropics, including many Pacific islands, southern and eastern Asia, and the Caribbean. The giant snail can now be found in agricultural areas, coastland, natural forest, planted forests, riparian zones, scrub and shrublands, urban areas, and wetlands.

Feeding[edit]

The giant African snail is a macrophytophagous herbivore; it eats a wide range of plant material, fruit, and vegetables. It will sometimes eat sand, very small stones, bones from carcasses and even concrete as calcium sources for its shell. In rare instances the snails will consume each other.

In captivity, this species can be fed on grain products such as bread, digestive biscuits, and chicken feed. It can be supplemented with calcium for shell development. It requires about 18.28% of crude protein in its diet for optimal growth.[10]

Life cycle[edit]

This species is a simultaneous hermaphrodite; each individual has both testes and ovaries and is capable of producing both sperm and ova. Instances of self-fertilization are rare, occurring only in small populations. Although both snails in a mating pair can simultaneously transfer gametes to each other (bilateral mating), this is dependent on the size difference between the partners. Snails of similar size will reproduce in this way. Two snails of differing sizes will mate unilaterally (one way), with the larger individual acting as a female. This is due to the comparative resource investment associated with the different genders.[citation needed]

Like other land snails, these have intriguing mating behaviour, including petting their heads and front parts against each other. Courtship can last up to half an hour, and the actual transfer of gametes can last for two hours. Transferred sperm can be stored within the body for up to two years. The number of eggs per clutch averages around 200. A snail may lay five to six clutches per year with a hatching viability of about 90%.

Adult size is reached in about six months, after which growth slows, but does not ever cease. Life expectancy is commonly five or six years in captivity, but the snails may live for up to ten years. They are active at night and spend the day buried underground.

Fresh eggs

Hatching from eggs

Juvenile snail

The giant African snail is capable of aestivating for up to three years in times of extreme drought, sealing itself into its shell by secretion of a calcerous compound that dries on contact with the air. This is impermeable; the snail will not lose any water during this period.[citation needed]

As an invasive species[edit]

In many places the snail is a pest of agriculture and households with the ability to transmit human and plant pathogens. Suggested preventive measures include strict quarantine to prevent introduction and further spread. It has been given top national quarantine significance in the United States.[6] In the past, quarantine officials have been able to successfully intercept and eradicate incipient invasions on the mainland USA.[13]

In the wild, this species often harbors the parasitic nematode Angiostrongylus cantonensis, which can cause a very serious meningitis in humans. Human cases of this meningitis usually result from a person having eaten the raw or undercooked snail, but even handling live wild snails of this species can infect a person with the nematode and cause a life-threatening infection.[14]

In some regions, an effort has been made to promote use of the giant African snail as a food resource to reduce its populations. However, promoting a pest in this way is a controversial measure, because it may encourage the further deliberate spread of the snails.

One particularly catastrophic attempt to biologically control this species occurred on South Pacific Islands. Colonies of A. fulica were introduced as a food reserve for the American military during World War II and they escaped. A carnivorous species (Florida rosy wolfsnail, Euglandina rosea) was later introduced by the United States government, but it instead heavily preyed upon the native Partula, causing the loss of most Partula species within a decade.